1. Field of the Invention
The present invention relates generally to seals for use in wellbores, and specifically to seals which include a plug member which sealingly engages a seat member to form a seal within a wellbore.
2. Description of the Prior Art
In the drilling, completion, and production of oil and gas wells, concentrically nested wellbore tubular members, such as casing, tubing, workstrings, and the like, define fluid flow paths. For business and engineering reasons, it is not uncommon for one or more wellbore fluid flow paths to be at least temporarily obstructed by the positioning of one or more valve plugs within the fluid path, which seat with valve seats disposed within the fluid flow path.
Commonly, shearable connectors, such as shear pins, are used in combination with the wellbore plug and valve seat to render a purposeful obstruction of a fluid flow path reversible. In practice, the wellbore plug sealingly engages the valve seat over a range of operating pressures. When a predetermined fluid pressure threshold is exceeded, shearable connectors are sheared, opening fluid paths around the combination of the wellbore plug and valve seat. Of course, this technique requires that the wellbore tubular member is equipped with ports or other fluid flow paths, which are expensive to design and manufacture, which present unacceptable risks of failure, and which can become clogged with debris carried in the wellbore fluids.
Prior art plug-and-seat valves present an additional problem. Frequently, the plug and seat assembly remain mated together, preventing the passage of wireline tools, workstrings, or coiled tubing through the wellbore tubular member. Of course, wireline tools and workstrings are now widely used for a number of wellbore operations, so obstruction by the plug-and-seat valve presents a serious impediment to standard wellbore operations.